Tractor-trailer brake system



May 23, 1961 w. sTELzER TRACTOR-TRAILER BRAKE SYSTEM 2 Sheets-Sheet 1Filed May 7, 1958 .IIJI

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May 23, 1961 w. STELZER 2,985,489

TRACTOR-TRAILER BRAKE SYSTEM Filed May 7, 1958 2 sheets-sheet 2 TE-EINVENTOR.

WILLIAM STELZ ER ATTORNEY United States Patent O TRACTOR-TRAILER BRAKESYSTEM William Stelzer, Bloomfield Hills, Mich., assignor toKelsey-Hayes Company, Detroit, Mich., a corporation of Delaware FiledMay 7, 1958, Ser. No. 733,575

18 Claims. (Cl. 303-23) This invention relates to a tractor-trailerbrake system, and more particularly to such a system whereinsuperatmospheric pressure is used for applying the tractor and trailerbrakes.

In conventional tractor-trailer brake systems, it is the common practiceto provide pedal controlled means for subjecting the tractor brakes todifferential pressures to apply such brakes, and to extend a serviceline from the tractor brake control means to` a relay valve mechanism onthe trailer so that changes in pressures in the tractor brake actuatorswill be communicated to the relay valve mechanism to operate it andconnect the trailer brake actuators to the source of pressuredifferential. It is well known that in such systems, the trailer brakesare applied to a degree proportional to the application of the tractorbrakes. The differential pressures to which the trailer brake actuatorsare subjected must be suiciently high to effect proper trailer brakeactuation when the trailer is heavily loaded, and as a result, excessivetrailer braking takes place when the trailer is running light or onlypartly loaded.

Moreover, it is also well known that an appreciable time lag occursbetween the application of the tractor brakes and the application of thetrailer brakes due to the interval of time necessary for pressuresignals to occur in the relay valvey through the service line. As aresult, the trailer brakes are applied after the tractor brakes, thusintroducing a serious operating condition which frequently causesjackkniting It is therefore the common practice to providetractor-trailer combinations with a hand valve in the cab of the tractorthrough the operation of which the driver may snub the trailer brakesindependently of the tractor brakes or anticipate the application of allof the brakes by operating the hand valve to apply the trailer brakesbefore depressing the brake pedal which controls the entire brakingsystem.

In my copending application Serial No. 726,666, led' April 7, 1958, nowPatent No. 2,941,844, I havevshown a novel type of electricallycontrolled auxiliary valve which is operative upon initial movement ofthe brake pedal from its normal off position to supply pressure to therelay valve to secure an immediate initial application of the trailerbrakes before the brake pedal is depressed to the extent necessary toapply the tractor brakes, thus eliminating the necessity for the use ofa hand valve and preventing the operation of the tractor brakes ahead ofthe trailer brakes.

An important object of the present invention is to provide a novel typeof electrically operated valve interposed between the air reservoir andthe relay valve on the tractor, by means of which diierent degrees oftrailer brake application can be provided in accordance with the loadingof the trailer.

A further object is to provide such a mechanism particularly adapted foruse with super-atmospheric pressure tractor-trailer brake mechanismswherein a normally inoperative valve mechanism is interposed in theservice line ahead of the emergency relay valve so that the latter ICCPatented May 23, 1961 is subject to operation in accordance with theapplication of the tractor brakes when the trailer is relatively heavilyloaded, and to provide novel means for operating the normallyinoperative valve mechanism to render it eiective for reducing thedegree of application of the trailer brakes when the trailer is runningunloaded or relatively lightly loaded.

A further object is to provide such a system wherein the normallyinoperative valve mechanism referred to can be controlled by the driverto reduce the eiective trailer braking when desired, and wherein suchvalve mechanism is automatically operative when so controlled topredetermine the maximum pressure supplied to the relay valve throughthe service line and thus predetermine the maximum degree of actuationof the trailer brake actuators.

A further object is to` provide such a system wherein the normallyinoperative valve mechanism referred to acts in combination with anautomatic auxiliary valve mechanism which functions upon initialoperation of the brake pedal to secure an immediate application of thetrailer brakes, and wherein the normally inoperative valve mechanism isinterposed in the service line between the auxiliary valve mechanism andthe relay valve of the trailer so that, whereas the auxiliary valvemechanism always operates in the same manner, its effect on the relayvalve is controlled by the normally inoperative valve mechanism topredetermine the degree of trailer brake actuation in accordance withthe loading of the trailer.

Other objects and advantages of the invention will become apparentduring the course of the following description.

In the drawings l have shown one embodiment of the invention. In thisshowing:

Figure 1 is a diagrammatic representation of the system as a whole;

Figure 2 is an enlarged axial sectional view through the normallyinoperative valve mechanism which may be controlled in accordance withthe loading of the trailer; and

Figure 3 is a similar view of the auxiliary valve mechanism whichfunctions to provide immediate trailer brake actuation upon initialmovement of the brake pedal from its normal olf position.

Figure l illustrates a tractor-trailer brake system of thesuper-atmospheric pressure type wherein a conventional control valvedevice 10 is connected as at 11 to the usual brake pedal 12 to beoperated thereby and apply the tractor brakes. To this end, the controlvalve device is supplied with superatmospheric pressure from an airreservoir 13 through a line 147 compressed air being supplied to thereservoir from a compressor 15 through a suitable line 16. Operation ofthe control valve device 10 supplies super-atmospheric pressure througha line 17, branched as at 18 for connection with the tractor brakeactuators 19 of conventional type. The line 17 extends rearwardlythrougha conventional connector 20 to supply fluid pressure through a serviceline 21 on the trailer. The usual emergency line 22 is also provided onthe trailer and is connected as at 23 tov a line 24 leading from the airreservoir 13.

The brake pedal 12 is connected as at 26 to an arm 27 carried by a disk28 frictionally engaged by a second disk 29 having an operating arm 30engageable with an arm 31 to close a normally open switch arm 32 toengage it with a contact 33 connected to one end of a line 34. Theswitch arm '32 is biased to open position by a' spring 35. The arm 31 isconnected to one terminal of a source 37 the other terminal of which isgrounded as at 38. Depression of the brake pedal 12 closes the switch32, and continued movement of the brake pedal beyond 'such point ispermitted because of the frictional engagement of the disks 28 and 29.When the pedal is released, the arm 30 will be frictionally returned tonormal position, at which point its movement is limited by a stop 39.This switch mechanism forms per se no part of the present invention andmay be of the type shown in the patent to Jeannot G. Ingres, No.2,571,885, issued October 16, 1951.

The trailer is provided with a conventional emergency relay valve 45,commonly known as a relay valve, and the emergency line 2.2 is connectedto such valve. In accordance with conventional practice, a break in theline 22, connector 23, or line 24 will operate the relay valve 45 toapply the trailer brakes, as will become obvious. A line 46 is branchedto supply fluid pressure to conventional trailer brake actuators 47operative to apply the trailer brakes. A pressure line 48 communicatesbetween the emergency relay valve 45 and air reservoir 49.

An auxiliary valve mechanism for effecting application of the trailerbrakes promptly upon initial movement of the brake pedal from its normaloil" position is indicated as a whole by the numeral 55 and is shown indetail in Figure 3 of the drawings. The auxiliary valve mechanismcomprises a preferably cast body 56 having a cylindrical bore 57 inwhich is axially movable a sealed plunger 8 provided with an axialpassage 59 therethrough. The lower end of the plunger 58 has anoutstanding ange 61 normally occupying the position shown in Figure 3 inengagement with a shoulder 62 formed in the body 56.

A diaphragm 65 is clamped to the bottom of the plunger 58 by a plate 66maintained in position by a nut 67. The periphery of the diaphragm isclamped to the body 56 by a lower cap 68 threaded into the body 56.

`Such cap forms with the diaphragm and associated elements a chamber 69in xed communication with the lower end of the axial passage 59. Thespace above the diaphragm 65 and around the plunger 58 is vented to theatmosphere as at 70.

A spring 74 is interposed between the bottom wall of the cap 68 and thenut 67 to bias the plunger 58 to its upper normal position shown. A stem75 extends loosely through the passage 59 and is provided at its upperend with a resilient valve 76 normally closing the upperend of thepassage 59 from the chamber formed in the Vupper end of the cylinder 57.A spring 77 biases the valve 76 to closed position.

The bottom of the cap 68 is provided with a port 80l to which theservice line 21 is connected. The port 80 communicates through a passage81 and valve seat 82V with the chamber 69. The valve seat 82 islengageable by a resilient valve 83 adapted to be closed in a manner tobe described to disconnect the chambers 69 and 80. The valve 8'3 iscarried by the lower end of the stem 75.

A check v-alve 86 is arranged in the bottom of the chamber 69 and hasits radially inner periphery seating against the bottom wall of the cap68. Radially outwardly of such portion of the check valve, a' passage 87communicates with the port 80 so that the bottom of the check valve 86is subject at all times to any pressure present in the service line 21.The check valve 86 may be in the form of Va stiiened diaphragm and isbiased to closed position by a spring 88.

A port 90 communicates at its upper end with the chamber 69 and has itslower end connected to one end of a line 91, the other end of which isconnected to a manually controllable valve mechanism described in detailbelow. The auxiliary valve mechanism 55 forms per se no part of thepresent invention, except in combination with the manually controlledvalve mechanism referred to, and is described and claimed in mycopending application Serial No. 726,666, fled April 7, 1958, now U.S.Patent No. 2,941,844, referred to above. In such copending application,the line corresponding to the line 91 leads directly to the relay valve45 to effect operation of the latter immediately upon initial operationof the brake pedal to activate the trailer brake actuators 47. In thepresent case, pressure signals through the line 91 are provided byoperation of the valve mechanism 55,V but the eiect of such impulses onthe emergency valve 45 is determined by the manually controllable valvedescribed in detail below.

In the top of the body 56 is formed a chamber 95 comrnunicating througha' passage 96 with the chamber 57. The body 56 is provided with a port97connected by a rline 98 to the air reservoir 49. The port 97 is adaptedto communicate through a passage 99 with the chamber 95, but suchcommunication is 4normal-ly cut olf by a resilient valve 100` carried bya stem 101. The stem 101 is connected to the armature 102 of a solenoid103. The space below the armature 102 is open to the atmosphere andnormally communicates with the chamber 95 through a port 104. Such portis formed in a closure plate 105 for the top of the chamber 95 andforms, around the port 104, a valve seat engageable by a normally openyresilient valve 108 carried by the stem 101. The armature 102 iS biaseddownwardly by a spring 109. One terminal of the solenoid 103 isconnected by a wire 1110 (Figure 1) through a detachable connector 111,with the wire 34. The other terminal of the solenoid is connected to awire 112 grounded as at 113'.

A manually controllable and normally inoperative valve mechanismindicated as a whole by the numeral 116 is connected' between the valvemechanism 55 and the emergency valve 45. The valve mechanism 116cornprises a preferably diecast body 117 having in the' upper portionthereof a chamber118. This chamber communicates with a port 119connected to the other end of the line 91 leading to the chamber 69 ofthe valve mechanismv 55.

The chamber 118 is formed in part by the upper end of a cylindrical bore120 in which is slidable Va sealed plunger 121 having a passage 122extending axially therethrough. The lower end of the plunger 121 isVformed as an enlarged head 124 movable upwardly into engagement with astop shoulder 125 formed iu the body 117.V The head 124 is normally inits lower position shown Vin Figure 2, spaced from they shoulder 125.The space between the upper and lower ends of the plunger 121 forms achamber 128 in which is arranged ya spring 129 Vwhich biases the plungerto its lower position shown in Figure 2.

A lower cap 132 is threaded on the body 117 and clamps in positiontherewith the peripheral portion of a diaphragm 133 iixed to the lowerplunger head 124 by a plate 134 normally engaging a shoulder 134 tolimit downward movement of the plunger 121.

Below the `diaphragm 133, a chamber 135 isformed in the cap 132, andthis chamber communicates with one end of a line 136 the other end ofwhich (Figure l) leads to the emergency relay valve. The chamber 135 isadapted to communicate with the atmosphere through a vent port I138normally closed by a resilient valve 139 carried by a stem 140projecting loosely through the axial passage 122. This stem is providednear its upper end with a resilient valve 141 normally disengaged fromthe upper lend ofthe plunger 121 and adapted to be engaged therewithunder conditions to be described to close communication through thepassage 122. A spring 142 biases the stem 140 downwardly to normallymaintain the valve 139 closed.

A passage 145 communicates at its lower end with the chamber 128 and atits upper end with a vertical passage 146 formed in the body 11-17 andnormally communicating at its lower end with the chamber 118. A solenoid147 is fixed above the body 117 and has an armature 148 carrying ahollow stem 149 provided yat its lower end with a resilient valve 150normally closing the upper end of the passage 146. The stem 149 carriesa depending stem 152 the lower end of which is provided with a valve 153normally opening the lower end of the passage 146 to the chamber 118 butmovable upwardly upon energization of the solenoid 147 to close thelower end of such passage. The armature 148 is biased downwardly by aspring 154 to normally maintain the valve '150 closed and the valve 153open.

One terminal of the solenoid 1147 is connected to a wire 156 grounded asat 157 (Figure 1). The other terminal of the solenoid 147 is connectedto the other end of the wire 157 which leads through a detachableconnection 158 to a preferably manually operable switch 159. The switch159 is connected by Ia wire 160 to the wire 34 previously described. Theswitch 159 is arranged in the open or heavy load position when thetrailer is relatively heavily loaded. When the trailer is unloaded orrelatively lightly loaded, the switch '159 is moved into engagement witha contact 161, under which conditions the impulses supplied from theauxiliary valve mechanism 55, through lines 91 and 136, to the relayvalve 45 will be limited to prevent maximum activation of the trailerbrake actuators 47.

Operation It will be assumed that the trailer is relatively heavilyloaded, in which case the switch 159 will be in the open or high loadposition shown in Figure l. Under such conditions, the solenoid 147(Figure 2) cannot be energized and the parts will all occupy the normalpositions shown. Under such circumstances, pressure impulses applied tothe pipe 91 by the valve 55, as described below, will render theemergency valve 45 initially subject solely to operation by theauxiliary valve mechanism 55. Pressure owing through the line 91 willenter the chamber 118 (Figure 2.), ilow through the passage 122 into thechamber 135, and thence through line 136 to the emergency valve. Thevarious passages, chambers and ports of the valve mechanism 116,therefore, will be connected in series with the lines 91 and 136, andthe system will operate in accordance with the disclosure of mycopending application referred to above.

Under such conditions, the operator, to apply the brakes, will depressthe bra-ke pedal 12 and initial movement of such pedal will close theswitch 32 to energize the solenoid 103 (Figure 3). The armature 102 willmove upwardly and the atmospheric port 104 will be closed by the valve108. At the same time, the valve 100 will be opened. Accordingly, thechamber 57 will be disconnected from the atmosphere and will beconnected through passage 99 and pipe 98 with the air reservoir 49.Fluid pressure in the chamber 57 will act on the upper end of theplunger 58 to move the latter downwardly, whereupon the spring 77 willseat the valve 83.-v The service line 21 thus will be disconnected fromthe chamber Slight further downward movement of the plunger 58 will movethe upper end of such plunger out of engagement with the valve 76, andfluid pressure will flow from the chamber 57 through passage 59 into thechamber 69 and thence through pipe 91 and through the various chambers,passages and ports of the valve mechanism 116, as described above, andthrough line 136 to the emergency relay valve 45 to energize actuators47.

It will be apparent that after initial movement of the brake pedal 12,operation of the control valve will supply super-atmospheric pressurefrom line 14 through lines 17 and 18 to the tractor brake actuators 19to start the application of the tractor brakes. Pressure also will flowthrough the service line 21. Due to the time lag necessary for pressurein the tractor brake actuators 19 to be reflected in the rear end of theservice line 21, the above-described operation of the auxiliary valvemechanism 55 will take place before substantial pressure has been builtup in the rear end of the serviceline 21. Thus any lag in theapplication of the trailer brakes is prevented, and these brakes will beapplied simultaneously with or slightly before the application of thetractor brakes, thus preventing any jaclckniing of the trailer withrespect to the tractor.

As soon as pressure in the rear end of the'line Ztl exceeds the downwardforce exerted against the check valve v86 by pressure in the chamber 69plus the loading of the spring 88, pressure will act on the bottom ofthe check valve 86 to move the inner periphery thereof upwardly for theow of air pressure into the chamber 69. This increased pressure in thechamber 69, acting on the bottom of the diaphragm 65, will move theplunger 58 upwardly the slight distance necessary to close the valve 76,thus disconnecting the chambers 57 and 69 from'each other. -When thepressure in the chamber 69 increases to a predetermined point, suchpressure will act upwardly on the diaphragm 65, whereupon the stem 75will be elevated. Thus the valve 83 willbe opened to directly connectthe port with the chamber 69, and pressure flowing out of the line 91will be the pressure affecting the tractor brake actuators 19. Suchpressure will be communicated to the relay valve 445 which functions inaccordance with conventional practice. Thus the trailer brake actuatorswill be activated to au extent proportional to the activation of thetractor brake actuators 19.

If, while the brakes are still being applied, pressure in the chamber 69should drop below a predetermined point, the plunger 58 will be moveddownwardly by pressure in the chamber 57. The Valve 83 will then closeand the valve 76 will be cracked to supply pressure lluid from thechamber 57 to the chamber 69. Differential pressures in the chambers 57and 69 thus prevent pressure in the chamber 69' from dropping below apredetermined point.

So long as the brake pedal is held depressed, the circuit through thesolenoid 103 will be maintained and the foregoing operations of theauxiliary valve mechanism 55 will take place. When the brake pedal 12 isreleased, the switch 32 will be opened and the solenoid 103 will bede-energized. Under such conditions, the chamber 57 again will beconnected to the atmosphere through passage 96, chamber 95 and port 104.Residual pressure in the chamber 69 will then promptly move the plunger58 to its uppermost position. The control valve 10 having been returnedto normal condition by the release of the brake pedal, there will be apressure drop in the service line 21. The opening of the valve 83incident to upward movement of the plunger 58 to the normal positionwill connect the line 91 to -the line 21, thus relieving pressure fromthe line 91 to restore the relay valve 45 to normal condition andrelease the trailer brakes.

Assuming that the trailer is running light or relatively lightly loaded,the operator will close the switch 159. With the brake pedal released,no circuit will be completed through the solenoid 147 since the switch32 will be open. However, immediately upon the depression of the brakepedal 12, the closing of the switch 32 willV not only energize thesolenoid 103 to cause the operation of the valve mechanism 55 in themanner described above, but will close a circuit through the solenoid147. Under such conditions, the armature 148 will move upwardly to openthe valve 150, and thus connect the chamber 128 to the atmosphere, andwill close the valve 153. This valve will have been previously normallyopen to connect and balance pressures in the chambers 118 and .128. Now,however, the closing of the valve 153 will connect the chamber 118solely to the line 91 leading to the auxiliary valve mechanism 55,previously described.. Therefore, when pressure is supplied through line91 by the operation of the valve mechanism 55, such pressure will flowthrough passage 122 into the chamber 135 to act against the bottom ofthe diaphragm 133 and move the plunger 121 upwardly. This operationcloses the valve 141. The action of the spring 129 is to somewhat delayupward movement of' the plunger 121 until adequate pressure has beenbuilt up in the chamber 135. As soon as the valve 141 is closed, noadditional Huid pressure can flow into the chamber 135. The pressuresupplied to the chamber 135 acts through the line `1136 on the relayYvalve, 45 to cause the normal functioning thereof to apply the trailerbrakes. The relative pressures in the chambers .118 and 135 will dependupon the relative areas of the yupper end of the plunger 121 and thearea of the bottom of the diaphragm 133i, which latter force is opposedto some extent by the spring y12,9. The several factors predeterminingrelative pressures in the chambers 120 and 135 can be asv desired sothat a lower pressure in the chamber `135 than in the chamber 118 willeffect operation of the relay valve 45.

From the foregoing, it will be apparent that when the switch 159 isopen, the valve 11-6 is inoperative for controlling pressures Iflowingbetween lines 91 vand 136. When :the switch 115,9 is closed, however,`when the trailer is relatively lightly loaded or empty, the pressure inthe line 136 will be lower to a predetermined extent than the pressurein the line 91, thus preventing .the over-application of the trailerbrakes under such conditions. The slight delaying of the closing of thevalve 141 assures adequate immediate pressures in the chamber 135 toeffect operation of the relayl valve'45. Any tendency for pressure inthe chamber 135 to increase above a predetermined point is preventedsince .such pressures will act upwardly on the diaphragm 133 to liftthestem 140 and thus crack the valve 139 to slightly vent the chamber 135to the atmosphere and restore the desired pressure therein.

Thus it will be apparent that the valve 55 will always function, so faras its Vown parts are concerned, solely in accordance with the operationof the brake pedal.

The results accomplished by the valve mechanism 55,

however, are determined by the operativenessV or inoperativeness of thevalve vmechanism 116. Whether the switch 159 is open or closed,therefore, the valve mechanism 55 functions to provide an immediateapplication of the t-railer brakes upon initial movement of the brakepedal from its normal off position. The functioning of the valvemechanism 55 for controlling the relay 'valve `45, however, isdetermined in accordance with the functioning of the valve mechanism116. 'I'hus irnmediate full application of the trailer brakes, orimmediate reduced application of the trailer brakes, will take placeupon operation of the brake pedal, depending on whether the switch 155is in the open or heavy load position or in the closed or light loadposition.

As previously stated, the valve mechanism 116 is preferably employed incombination with the valve .mechanism 55 because of the advantageousresults obtained, namely, .both the quick initial setting of thevtrailer brakes and the limiting of the energization of the trailerbrake actuators when the trailer is running light. It also will be notedthat the valve mechanism 116, controllable in accordance with thetrailer load, is capable of being used in a conventional system withoutthe valve mechanism 55. In such case, the valve mechanism 55 andassociated elements would be eliminated, andthe service line 21 Vandpipe 91 are directly connected to each other.

It is to be understood that the form of the invention shown anddescribed is to be taken as a preferred example of the same and thatvarious changes in the shape, size, and arrangement of the parts may bemade as do not depart from the spirit of the invention or the scope ofthe -appended claims.

`I claim:

l. In a tractor-trailer brake system, brake actuators for the tractorbrakes, manually operable control means on the tractor for supplying uidpressure to said actuators, actuators for the trailer brakes, a relayvalve on the trailer connected to said trailer brake actuators andoperable for supplying fluid pressure to said trailer brake actuators4from a source of pressure on the trailer, a service line connected atone end to said control means Vand at its other end to said relay valveto render the latter operable when pressure is present in said service`sure area subject` topressures in said other end of said service line,a valve device having mechanical engagement with said pressureresponsive unit and having a normal position opening communicationbetween said ends of said service line, and selectively operable meansconnected to said control means for operation therewith for renderingpressure in said other end of said service line effective against saidrelatively larger pressure area for moving f said pressure responsiveunit from said normal position to close said valve device and limit thebuilding-up of pressures in said other end of said service line.

2. A system according to claim l wherein said means for renderingpressure in said other end of said service line effective for movingsaid pressure responsive unit from said normal position comprises avalve device connected for operation with said control means andoperable for rendering pressure in said other end of said service lineeffective against said larger area of said pressure responsive unit formoving the latter away from said normal position.

3. A system according to claim 1 wherein said means for renderingpressure in the other end of said service line eifective for moving saidpressure responsive unit from said normal position comprises anelectromagnetic device, and a switch connected for operation by saidcontrol means for closing a circuit through said electromagnetic device.

4. In a tractor-trailer brake system, brake actuators for the tractorbrakes, manually operable control means on the tractor for supplyingfluid pressure to said actuators, actuators for the trailer brakes, arelay valve on the trailer connected to said trailer brake actuators andoperable for supplying fluid pressure to said trailer brake actuatorsfrom a source of pressure on the trailer, a service -line connected atone end to said control means and at its other end to said relay valveto render the llatter operable when pressure is present in said serviceline, and a valve mechanism connected in said `service line andcomprising a body having a rst chamber communicating with said one endof said service line and a second chamber communicating with said otherend of said service line, a pressure responsive unit having a relativelysmall surface exposed to said iirst chamber and a relatively largesurface exposed to said second chamber, a normally open valve devicehaving mechanical engagement with said pressure responsive unit, saidpressure responsive unit having a normal position in which said valvedevice provides communication between said chambers whereby pressureimpulses in said one end of said service line will pass'to said otherend of such line to operate said relay valve, means biasing saidpressure responsive unit to said normal position, said valve mechanismhaving a third chamber to which another surface of said pressureresponsive unit is exposed to oppose pressure acting against saidrelatively large surface, passage means communicating between said iirstand third chambers, and valve means for closing said third chamber tosaid first chamber and opening said third chamber to the atmospherewhereby pressure acting against said larger surface will move saidpressure responsive unit to close said valve device to limit thebuilding-up of pressure in said other end of said service line.

5. A system according to claim 4 wherein said means for closing saidthird chamber to said `first chamber and opening said third chamber tothe atmosphere comprises a normally open valve element between saidpassage means and said first chamber and a normally closed valve elementbetween said passage means and the at- 9. mo'sphere, and means formoving said valve elements to close said normally open valve element andopen said normally closed valve element.

6. A system according to claim wherein said means for moving said valveelements comprises an electromagnetic device connected to said valveelements, and a circuit for said electromagnetic device comprising aswitch.

7. A system according to claim 5 wherein said means -for moving saidvalve elements comprises an electromagnetic device connected to saidvalve elements, a brake pedal connected to said control means and havinga normal olf position, and a circuit for said electromagnetic devicecomprising a pair of switches in series, one of said switches beingconnected to said brake pedal to be closed upon initial movement thereoffrom its oi position, the other of said switches being operableindependently of said one switch.

8. In a tractor-trailer brake system, brake actuators for the tractorbrakes, a brake pedal on the tractor having a normal ol position,control means on the tractor connected to said brake pedal and operablefor supplying fluid pressure to said actuators, actuators for thetrailer brakes, a relay valve on the trailer connected to said trailerbrake actuators and having a uid conduit connected to a source of uidpressure on the trailer, a service line connected at one end to saidcontrol means and at its other end to said relay valve whereby pressurein said service line will operate said relay valve to supply pressurefluid from said source to said trailer brake actuators, an auxiliaryvalve mechanism connected in said service line and comprising elementsconnected for operation by said brake pedal and operative upon initialmovement of said brake pedal from ofI position for supplying pressurefluid from said source to said other end of said service line to operatesaid relay valve and comprising other elements connected to beresponsive to pressure in said one end of said service line and operablewhen pressure in said one end of said service line increases to apredetermined point for closing communication between said source andsaid other end of said service line and opening communication throughsaid service line, and a second valve mechanism connected in saidservice line and normally providing for the free ow of fluid throughsaid service line, said second`valve mechanism comprising controllableelements for reducing pressure supplied through said service line fromsaid auxiliary valve mechanism to said relay valve.

9. A system according to claim 8 wherein said controllable elements ofsaid second valve mechanism comprise normally inoperative pressureresponsive means having areas exposed to pressures respectively in saidends of said service line and opening communication through said serviceline, and means for rendering said pressure responsive means responsiveto pressure in said other end of said service line so as to becomeoperative for relatively reducing pressures owing from said auxiliaryvalve mechanism to said relay valve.

l0. A system according to claim 8 wherein said controllable elements ofsaid second valve mechanism comprise normally inoperative pressureresponsive means having areas exposed to pressures respectively in saidends of said senvice line and opening communication through said serviceline, a chamber normally communicating with said one end of said serviceline, said pressure responsive means having a third area open to saidchamber to oppose movement of said pressure responsive means by pressurein said other end of said service line, a valve device for normallymaintaining said communication between said chamber and said one end ofsaid service line, and means for operating said valve device for closingcommunication between said one end of said service line and said chamberand opening said chamber to the atmosphere for rendering said pressureresponsive means operative for reducing pressures passl0 ing throughsaid service line from said auxiliary valve mechanism to said relayvalve.

1l. A system according to claim 8 wherein said controllable elements ofsaid second valve mechanism comprise normally inoperative pressureresponsive means having areas exposed to pressures respectively in saidends of said service line and opening communication through said serviceline, a chamber normally communicating with said one end of said serviceline, said pressure responsive means having a third area open to saidchamber to oppose movement of said pressure responsive means by pressurein said other end of said service line, a valve device for normallymaintaining said communica- 4tion between said chamber and said one endof said service line, an electromagnetic device connected to said valvedevice to operate it to close communication between said one end of saidservice line and said chamber and open said chamber to the atmosphere torender said pressure responsive means responsive to predeterminedpressure in said other end of said service line to be moved by suchpressure to prevent further flow of fluid through said service line, anda circuit for said electromagnetic device comprising a pair of switchesin series, one such switch being connected to said brake pedal to beoperated upon initial movement thereof from normal oi position and theother switch being operable independently of said one switch.

l2. In a tractor-trailer brake system, brake actuators for the tractorbrakes, a brake pedal on the tractor having a normal off position,control means on the tractor connected to said brake pedal and operablefor supplying iluid pressure to said actuators, actuators for thetrailer brakes, a relay valve on the trailer connected to said trailerbrake actuators and having a fluid conduit connected to a source offluid pressure on the trailer, a service line connected at one end tosaid control means and at its other end to said relay valve wherebypressure in said service line will operate said relay valve to supplypressure fluid from said source to said trailer brake actuators, anauxiliary valve mechanism connected in said service line and comprisingelements connected for operation by said brake pedal and operative uponinitial movement of said brake pedal from oil position for supplyingpressure uid from said source to said other end of said service line tooperate said relay valve and comprising other elements connected to beresponsive to pressure in said one end of said service line and operablewhen pressure in said one end of said service line increases to apredetermined point for closing communication between said source andsaid other end of said service line and opening communication throughsaid service line, and a second valve mechanism connected in saidservice line between said auxiliary valve mechanism and said relay valvemechanism, said second valve mechanism comprising a body having apressure responsive unit therein having a relatively large surfaceexposed to pressure in said other end of said service line and a surfaceof relatively small area exposed to said service line between saidauxiliary and said second valve mechanisms, said second valve mechanismhaving a normally open passage for the flow of fluid through saidservice line, a valve element mechanically connected to said pressureresponsive unit and arranged to close said passage upon movement of saidpressure responsive unit from a normal position by pressure acting onsaid relatively large surface, and a selectively operable means forrendering pressure to which said large surface is exposed operative orinoperative for moving said pressure responsive unit from normalposition.

13. A system according to claim 12 wherein said selectively operablemeans comprises an electromagnetic device, and a circuit for saidelectromagnetic device comprising a pair of switches in series, one ofsaid switches being connected to said brake pedal to be closed uponinitial movement of said pedal from said oi position,

1l the other switch being operable independently of said one switch.

14. In a tractor-trailer brake system, brake actuators for the tractorbrakes, a brake pedal on the tractor having a normal off position,control means on the tractor connected to said brake pedal and operablefor supplying Huid pressure to said actuators, actuators for the trailerbrakes, a relay valve on the trailer connected to said trailer brakeactuators and having a fluid conduit connected to a source of fluidpressure on the trailer, a service line connected at one end to saidcontrol means and at its other end to said relay valve whereby pressurein said service line will operate said relay valve to supply pressurefluid from said source to said trailer brake actuators, an auxiliaryvalve mechanism connected in said service line and comprising elementsconnected for operation by said brake pedal and operative upon initialmovement of said lbrake pedal from off position for supplying pressureluid from said source to said other end of said service line tooperatesaid relay valve and comprising other elements connected to beresponsive to pressure in said one end of said service line and operablewhen pressure in'said one end of said service line increases to apredetermined point for closing communication between said source andsaid other end of Said service line and opening communication throughsaid service line, and a second valve mechanism connected in saidservice line between Vsaid auxiliary valve mechanism and said relayvalve, said second valve mechanism comprising a body having a firstchamber and a second chamber communicating respectively with said otherend of said ser-vice line and with said service line between saidauxiliary and said second valve mechanisms, a pressure responsive unitin said body having a larger surface exposed to said rst chamber and asmaller surface exposed to said second chamber, said pressure responsiveunit having a passage therethrough normally connecting said chambers, anormally open valve arranged adjacent said `smaller surface andengageable thereby when said pressure responsive unit moves from anormal position by pressure acting on said larger surface to closecommunication through said passage, means normally operative forrendering pressure in said second chamber inoperative for moving saidpressure responsive unit, and selectively operable means connected tosaid last-named means for rendering said last-named means inoperativewhereby pressure in said second chamber will move said pressureresponsive unit to close said normally open valve.

l5. A system according to claim 14 wherein said selectively operablemeans comprises an electromagnetic device and a circuit for saidelectromagnetic device comprising a pair of switches in series, oneswitch being conf nected to said brakeV pedal to be closed thereby whensaid brake pedal initially moves from oi position and the other switchbeing operable independently of said one switch.

16. A system according to claim 14 wherein said means normally operativefor rendering pressure in said second chamber inoperative for movingsaid pressure responsive unit comprises a third chamber to which isexposed a surface of said pressure responsive unit opposing said largersurface, and means normally connecting said third chamber to said rstchamber, said selectively operable means comprising mechanism forclosing said third chamber to said rst chamber and opening it to theatmosphere to eliminate pressure in said third chamber opposing pressurein said second chamber.

17. A system according to claim 16 whereinv said lastnamed mechanismcomprises passage means communicating with said third chamber, anormally open valve element connecting said passage means to said firstchamber, a normally closed valve element closing communication betweensaid passage means and the atmosphere, and lmeans for moving said valveelementsV to close said normally open valve element and open saidnormally closed valve element.

18. A system according to claim 16 wherein said lastnamed mechanismcomprises passage means communieating with said third chamber, anormally open valve element connecting said passage means to said rstchamber, a normally closed valve element closing communication betweensaid passage means and the atmosphere, a normally de-energizedelectromagnetic device connected to said Valve elements, and a circuitfor said electromagnetic device comprising a pair of switches in series,one of which is connected to said brake pedal to be closed upon initialmovement thereof from oi position and the other of which is normallyopen and adapted to be closed independently of said one switch.

References Cited the file of this patent UNITED STATES PATENTS 2,062,500Casler et al. Dec. 1,1936 2,362,931 Rodway Nov. 14, 1944 2,808,902Williams Oct. 8, 1957

